Max SSD capacity of Dell Precision 7730 i7-8850H

Unfortunately, you can not install all 4 NVMe SSD on your laptop, just 3.  Slot 4 uses SATA.

Any well known brands available in your markets should be suffice.  Samsung, SK Hynix, Crucial (Micron), etc.  Get whichever drives that can give you best value.  Note that Gen 4 drives will be performed at Gen 3 speed.

weird...on the spec sheet (https://i.dell.com/sites/csdocuments/Product_Docs/en/precision-7730-spec-sheet.pdf) they mention that it supports four m.2 pcie? Are there 2 models with different motherboards? Also, 2 tb is listed as maximum capacity.

Support for 4 storage devices: Four M.2 PCIe solid state drives or three M.2 PCIe solid state drives and one 2.5” SATA SSD/HDD drive: Dell Fast Response free fall sensor standard
Hard Disk Drive (HDD): 2.5” 500GB, 500GB FIPS SED (Check regional availability), 1TB 7200RPM up to
2TB 2.5” 5400RPM SATA 6Gb/s
Solid State Drive (SSD): 256GB, 512GB, 512GB SED (Check regional availability), 1TB 2.5” SATA 6Gb/s
M.2 PCIe NVMe Solid State Drive (M.2 SSD): 256GB, 512GB, 512GB SED, 1TB SED (Check regional availability), 1TB, 2TB SSD

That's correct, the 7730 can support four M.2 PCIe solid state drives form factor.  But, one (on slot 4) must be M.2 AHCI (SATA protocol).  See the bottom notation on storage specifications screengrab.

@Chino de Oro​ thank you for the info